Membrane associated receptor proteins appear to be involved in the mechanisms by which cells "sense" and respond to small molecules. An understanding of hormone action or the functioning of chemically excitable post-synaptic nerve membranes will require a detailed knowledge of such membrane receptors. At the present the best characterized reception systems are probably the chemoreceptors involved in chemotaxis by Escherichia coli. Because of the genetic and biochemical techniques which are available, those receptors could be the first to be understood in detail. This proposal is concentrated on the study of the maltose receptor of E. coli. That receptor functions to enable the cell to be attracted to maltose. Two protein components of the receptor have already been identified and can be purified. A genetic search will be made for additional components. The interactions between the receptor components, at least one of which is known to be tightly associated with a membrane, will be characterized both genetically and biochemically. The unusual features of the binding of maltose to the binding protein which serves as the recognition component for the receptor will be studied with the hope of understanding the mechanism by which the bacteria detect a temporal gradient of the attractant. Hopefully the pattern of interactions between receptor components will reveal the means which binding information is transferred from the binding protein through the receptor, to affect the movement of the bacteria.